Integral imaging is a form of three-dimensional imaging, and, along with holography and lenticular photography, are the three auto-stereoscopic methods of three-dimensional imaging (stereo imaging without the use of special glasses).
Over the years, numerous auto-stereoscopic devices and methods have been devised for producing images having all four physiological depth perception cues. The physiological cues are summarized in THREE DIMENSIONAL IMAGING TECHNIQUES (T. Okoshi, Academic Press 1976) and they are: accommodation, convergence, binocular parallax, and monocular movement parallax.
Accommodation is a cue given by the adjustment of the focal length of the eye's crystalline lens when an eye focuses on a particular object. Convergence is a cue given by the angle made by the two viewing axes of observer's eyes. Binocular parallax is a cue caused by the difference between the views seen by the two eyes of an observer. Monocular movement parallax is a cue observed when a person is moving and is caused by the changing view in each of the person's eyes. Accommodation and monocular parallax are available even when we see an object with a single eye.
There are several stereoscopic techniques that provide at least one of the physiological depth cues. Binocular stereoscopic technique is based on the idea that when two slightly different images are provided to two eyes of an observer then the binocular parallax will be observed. However, this technique does not provide any of the other three physiological cues.
Holography is a technique that reproduces all four physiological cues. Unfortunately, it is very difficult to generate and produce a synthetic hologram because a very fine interference pattern needs to be computed and reproduced. This makes it difficult to implement an auto-stereoscopic display based on the holography principle. Another disadvantage of the holography approach is that it records and reproduces a monochromatic light, thus the reproduced image has one dominant color.
Another stereoscopic image reproduction method is called parallax barrier technique. This method is based on the idea of showing different images on a display through a blocking barrier that has only one vertical slit open at a time. Each open slit has certain image shown through it. This technique, however, reduces display resolution and results in a low light display since the parallax barrier blocks most of the light.
Numerous efforts were made trying to create a stereoscopic display based on above techniques in combination with eye tracking methods. Eye tracking was part of the invention of a binocular screen that does not require any special glasses as in the U.S. Pat. No. 5,349,379. Eye tracking also allowed other researchers to optimize parallax barrier display. However, the disadvantages shown above still remain for every aforementioned type of the stereoscopic display.
Integral photography or integral imaging is another method that like holography provides all four physiological depth cues. However, images displayed using Integral Imaging methods are much easier to generate and to reproduce than hologram interference patterns.
Integral photography was first proposed by the physicist, Gabriel Lippmann, in 1908 to the French Academy (Lippmann, M. G., Compt. Rend. Acad. Sci. Vol. 146, 446 (1908)). Lippman proposed a method to record a complete spatial image on a photographic plate, with parallax in all directions, utilizing an array of small spherical convex lenses, all in a single exposure. In this method, later known as the direct method, an object or scene is recorded directly in front of the lens array.
Lippman performed several crude tests of his proposed method. In one test he used an array of 12 small lenses mounted in a rectangular frame. He stated that “in illuminating the plate one no longer sees individual microscopic images; they are replaced by a single (integral) image, which is seen under the same angle as the original subject.” He went on to report that the resulting image changes form, just like the original object itself, depending on the position of the viewer, and also changes its angular dimensions with distance. (Lippmann, M. G., J. Soc. Franc. Phys, Vol. 69 (1912)).
Lippmann's theoretical suggestions, however, turned out to exhibit some fundamental problems when efforts were made to implement the concept by other researchers. Most importantly, the image as seen by the observer appeared pseudoscopic, having a reversed depth, where the foreground becomes the background and vice versa.
Later, one of the primary researchers of Integral photography was Roger de Montebello. His patented Integram process included extensive work on manufacturing lens arrays for viewing and for a two-step process camera. (see U.S. Pat. No. 3,503,315 which is incorporated by reference in its entirety). The camera was used to take the pseudoscopic image and for reversing the image to get the virtual image.
Thus, Roger de Montebello used an optical process to reverse the pseudoscopic image to get the virtual image with normal parallax. He did this by using the same camera to make the original image in a different configuration. The main problems with his process were as follows:
When reversing the image, the dark regions between the elemental images were visible in the final integrated image causing a “Chicken Wire” flaw viewable on top of the virtual image. Roger de Montebello tried to remedy this flaw by magnifying the images to reduce the size of the dark regions. However there was a limit to the possible magnification elemental images with his process because images would start to overlap neighboring elemental images.
Integrams also suffered from a somewhat narrow viewing angle. At certain viewing angles the virtual image would gradually flip to an entirely different virtual image over several degrees of viewing angle. This was called the “Imperial Crown Effect.” The flip would occupy several degrees of viewing angle where the two images would chase each other.
Although a lot of work has gone into integral imaging, there are still numerous issues that prevent application and commercialization of this method of producing three-dimensional images. These problems include the “Chicken Wire” flaw and the “Imperial Crown Effect.”
Research in this field later led to inventions of various displays based on the same principle of Integral Photography such as CRT and LCD auto-stereoscopic displays. All of these inventions, however, either exhibited same problems as de Montebello's device or proposed means to correct these problems which were not technically possible or were not commercially feasible.
Yet other devices of the prior art function using time multiplexing, requiring complex timing operations in the display system. Further, such display systems of the prior art are often cost-prohibitive.
Integral imaging consists of a two-dimensional array of distinct small images that is viewed by the observer through a lens array of spherical convex lenses. Each lens of the lens array sits on top of each image of the image array. When viewed together the images integrate into a unified image which mimics an actual light wavefront coming from a imaged object, and provides the viewer with a three-dimensional image which they move around and see different views.
Integral imaging provides benefits not seen with either holography or lenticular photography. Unlike holography, the local color of the subject in the image is not lost in integral imaging, and is as true to color as conventional photography.
Likewise, in lenticular photography the viewer sees dimensionality only from side to side or up and down, but not both in the same photograph. Thus, unlike lenticular photography, the three-dimensional effect of integral photography can be observed in all directions.
Thus, integral imaging had great potential to produce three-dimensional still and video images that could be used for a host of applications, including advertising, animations, art, video games, portraiture, still lifes, supplemental educational tools, home photos, dimensionalize consumer snapshots. However, up to now nobody could successfully produce high quality images that did not suffer from the problems listed above.
As can be seen, there is a need for a device and method that produces an auto-stereoscopic, three-dimensional image of superior quality, the image having all four physiological depth perception cues, as previously described. It is desirable to produce such an image without excessively limiting one's field of view of such an image. It is further desirable to readily and economically produce and generate such an image.